This was the first draft copy of a technical description of the snatch, aimed at the lifter rather than the coach. This is not the complete or final version (sadly my laptop is on the blink so this is the only drft from my tablet. There may be small mistakes (it was a rush job), but no major ones:

A Technical Description of the Snatch for the Athlete

Generally in specialist literature, technical descriptions of the competition lifts are targetted at coaches, biomechanists and sports physiologists for technical analysis and further improvement of technique. However, such descriptions are not well suited to the athlete themselves. This guide, although helpful to the above, is written with the athlete themselves in mind in addition to, but not replacing, correct coaching.
An important note is that the lifter should always think of the body and barbell as a single system, with its own centre of gravity, and focus on perfecting movement of the body rather than simply lifting the bar.
J.H.

The Start Position
Description of the Squat Snatch
Performance of the Squat Snatch

The Start Position

The start position is dynamic, in that it is part of the lifting itself and not merely for preparation. It is vital to successful lifting that this position be mastered to the point where it becomes a natural, unconscious position.

At the moment of the start, the athlete is positioned with the major joints at the most advantageous angles:

The thighs are at an angle of between 90°-100° to the calves. This ensures that at the beginning of the lift the athlete is able to start with the lowest position creating more time and distance for power production, but avoiding slowing during the middle phase of thigh extension. Essentially the lifter is beginning at the 'slowest' position and accelerating. This position will also aid the balance of the lifter.

The torso is held staticly either completely straight or with a slight lumber curve at an angle of 30° to the floor. This provides a strong link preventing loss of force transfer from the legs to the bar. At the same time it allows the major joints to work more efficiently in changing the position of the body.

The bar is directly above the joints between the toes and ball of the foot. This bar position allows for the shins to come forwards and the athlete-weight system to maintain a combined cenre of gravity.

The shins are angled forwards so that they just touch, but do not press into the bar. This position allows for the greatest combined balance possible.

The head is eased back slightly so as to increase the tension down the spine.

The feet are flat against the floor with the weight evenly distributed across their base. This point must be emphasised - the greatest area of balance is the ideal. Foot width should be in the most advantageous position to create upward force. The ideal is between directly under the hips and directly under the shoulders. The outside edges of the middle foot should not be outside the limit of the clavical, wheher feet are directed forwards or with toes slightly outwards.

The deltoids and trapezius are relaxed and allowed to hang in front of the bar. A slight pectoral contraction helps to maintain the forward position of the deltoids, and allign the elbows horizontally, the elbows pointing along outwards the bar.

The arms are at a slightly backwards angle towards the bar, helping to maintain the positions described and a result of the best balanced body position.

The upper arms are relaxed. This should remain so until the point where they need to come into play during the pull phase of the snatch. Unnecessary tension in the upper arms inhibits correct bar movement.

The hands have gripped the bar at the optimal point which the body position allows without excessive tension in the upper limbs.

Methods of Establishing Grip Width

The best methods of establishing grip width are as follows:
The elbows are held directly outwards and the space between the fore finger and middle finger matches this width.

The body is in the correct starting position with the hands as wide as the position allows, then brought in between 1" and 3" to ensure upper limb relaxation.

In both cases the lifter should adjust the hand spacing according the individual preference, bearing in mind the following:

It should be noted that the wider the hand grip, the greater the disadvantage in applying upward force to the barbell. At the same time closer grips mean the bar must travel a greater distance from the explosion to arms extended overhead. The closer grip is preferable depending on the lifter's spine and shoulder flexibility so as to increase the power transferred to the bar. The caveat here is that the higher the final position of the bar overhead, the higher the centre of gravity of the athlete-weight system. For this reason a compromise erring on the closer width is best.

The athlete is advised to practice holding this starting position to perfect the necessary motor awareness and therefore 'feel' of the correct position. This will enable the lifter to begin lifting the bar in the same position despite any other pre-lifting movements.

Of utmost impotance in the start position, as during the lift itself, is the balance between muscle tension and relaxation. The start position is in fact part of the lift rather than simply a preparatory position. Therefore in this position relaxation should be highest, especially in the arms and shoulders. This initial impulse which lifts the bar is a sudden, rapid and forceful contraction of the legs pushing the flat feet through the floor causing the first reactive force, that of extending the legs and the body rising. It is vital that the feet maintain the weight across their base during the upwards portion of the movement to maintain the best balance and maximum force against the floor.

The Movement of the Snatch - Explanation

The movement of the snatch begins with the start position and ends when the bar is held at arms length above the head in a standing position. The athlete should not think of the movement in stages, which is an artificial system used for technical analysis. What follows is a description aimed at the athlete and personal coach.

At the first instant of the upward movement, the lifter is either stationary or already moving but in the start position the moment the bar leaves the floor. This is achieved by a rapid, forceful contraction of the quadriceps driving the floor away through the feet, much like a leg press. The reactive force lifts the athlete-weight system. The athlete should not think of this movement as a 'pull'.
It is important that while rising the lifter initially eases the hands and barbell backwards towards the body. It should be noted the aim is not to press the bar into the shins and drag the bar along them. Rather the bar follows the path of direction of the shins, backwards and stays in close.
There are two good methods of achieving this:
The first is easing the relaxed but straight arms backwards whch results in a slightly forward motion of the shoulders.
The second is a perculiar technique, and little known, and is achieved thus:

During the lifting of the barbell, the arms and torso remain in their initial positions, the upper arms relaxed. However, to follow the correct bar path, the wrists are flexed early, creating a slight backwards shift of the bar which is followed by the arms. This is the same motion carried out by the wrists when the lifter tugs the elbows back at the transition of the upwards-downwards motions. What can be seen is as the bar rises past the knees the tension created by this wrist flexion causes a slight bending of the arms. This flexed wrist position should be maintained for the rest of the movement because re-exrending the wrists will a) shift the bar back away from its optimal path, and b) re-straighten the arms losing bar velocity, height and upwards force.

While both methods differ slightly in their mechanics, there is no current evidence of either being superior. However, from a point of view of efficiency, the latter method would appear the better of the two. There is a second benefit to this method in that a small impulse is added to the bar during the middle range of the upward phase where speed drops. This helps to maintain bar speed, and for this reason it is suggested this is the better method.

The forcing away of the ground is carried out at any rate with the torso maintaining its angle of 30° (actually 28-31° depending on thr relative torso length of the lifter. Longer torso relative to limbs can accomodate the shallower angles). The speed of pushing should begin fast and accelerate during this movement. Doing so rapidly induces a stretch in the hamstrings, gluteal muscles and muscles of the rear calf. This allows for the second of the reactive forces during the movement: the stretch reflex of the above muscles. When the legs are almost fully extended, the tension can be felt and begins pulling the torso into a more upright position. Any loss of isometric tension along the back will reduce this effect and lead to loss of force transfer to the bar.
The continued reactive force is as follows:
As the hamstring group and muscles of the calf react to the sudden stretch, they contract in the opposite direction. This of course leads to a momentary loss of velocity as the contraction of the quadriceps is anatognised, essentially acting as a brake. The next effect is that the torso is pulled upwards, and more importantly the knees are shifted forwards and the hips and knees together downwards. This phenomenon is often referred to as the "double knee bend" and is a useful indicator for the lifter and observer of a correctly performed lift. This movement is also purely a biomechanical reaction and should not be consciously performed.

Much has been written of the correct bar path during the squat snatch, and various lifters often film their lifts from one side to monitor the path and then attempt to perform corrections. The lifter should be warned of this, as this bar path is of use to coaches only in establishing the most likely part of the lift causing the error. The self-correcting lifter is likely to pull the bar backwards to correct a wide path, resulting in inefficient technique. Rather the lifter should be concerned with improving an entire complex movement and any 'specific' errors corrected by an experienced coach.

As the knees shift under the bar the lifter must achieve the most difficult action of the upward phase - the rapid switching of tension from the quadriceps to the hamstrings.
The relaxation of the quadriceps allows for faster tension, already existing, to occur in the hamstrings. The hamstrings and gluteal muscles are then used to force the hips inwards and upwards, the upwards movement being accentuated in the squat snatch as opposed to the forward motion in the split snatch. It is whilst this movement is occurring that the major contact between bar and body occurs - that of the bar "polishing" the thighs.

It is important that the lifter be aware that the bar should not be pulled in towards the body with the arms, pulled along the thighs or into the hip. Doing so shifts balance upwards and backwards result in a throwing of the bar forwards with the thighs or hips. The bar will move back towards the cenre of the base as the body moves towards vertical, with no extra pulling movements.

Whilst this is still occurring, the quadriceps are re-utilised to aid the hamstrings in pulling the knees in. This is important because of the desired action:
Whilst the hips are travelling towards the bar path, the knees are still under the bar and the torso is moving towards upright. Should the knees remain forwards when the hips are in line with the feet and the torso is upright, the centre of gravity is shifted forwards. The result of this is that the athlete-weight system is pulled forwards, the base area is reduced to the front of the foot and the lifter must move against the weight in order to maintain a balanced system. The lifter pulls back with the shoulders changing the momentum of the bar from going upwards to going backwards. This slows the upward motion, reduces eventual height and destroys the balance. The knee and hip movement is to create and upward drive of the whole system. Doing this with sufficient power will allow the continued upward path, and allow the lifter to rip, or rapidly peel the feet from the floor to re-establish a new, wider, base. This should not be perceived as a 'jump', nor should the lifter endeavour to create additional height once the hip action is completed by pulling up with the shoulders or arms or rising up onto the toes. The flexion of the ankle is reactionary. It should go without saying that the hips are not used to throw the bar, as this will create an outwards movement of the bar.

Once the hips and knees have been brought into line over the base, the work to move the body upwards is completed and the lifter must rapidly switch directions to move downwards.

The feet will have left the floor if enough power has been applied through the legs and hip movement, and this should not be excessively high. Therefore no attempt at further upwards extension of the body should be used to add height. The opportunity should be made to adjust the base for the following reason:
When the lifter has the bar in the final position, the combined centre of gravity is towards the heavier part of the system, and therefore much higher. A heavy bar will also travel a shorter distance on momentum against gravity. For both these reasons it is in the interests of the lifter to gain the lowest and most stable position. For this, the base must be eidened to increase the area of support and to allow the hips to get as low as possible while remaining balanced. Therefore the feet are repositioned further apart and the toes moved to point outwards. Although the exact extent varies from person to person due to difference in mobility, leverage, limb length and leg strength, a general rule is to place the feet just wider than shoulder width, and toes no more than 45° outwards. The feet should also land flat on the floor, but not driven in to the floor.

The ripping of the feet, in what may seem counter intuitive, is actually part of the downwards descent of the lifter. During this moment the lifter aggressively begins pulling their body downwards but does not restrain the movement of the bar in any way. If the upwards movement has been correctly performed, the bar will be travelling at high speed in a close to vertical line upwards, close to the body. As soon as the hips have finished moving in, the feet are torn from the floor as already mentioned. The lifter moves the body by continuing the leg flexion with the hamstrings, shoving the body downwards and using arm movement to create another reactive movement:

Whilst the body is starting to move downwards at high speed, it will be possible for the lifter, given correct barbell trajectory and speed, to slightly loosen the grip on the bar. This will increase the relaxation of the whole arm, allowing them to bend easily under the impulse of the moving barbell. As the body is moving down, the lifter assists the body movement by tugging the elbows upwards. This also creates a reaction which adds a small impulse to the already moving bar, and also affects the path of barbell direction. For this reason it is imperative that the lifter has maintained the position of the arms with elbows pointing sideways, the muscles relaxed and that the elbows move upwards but without using high amounts of force from the biceps. This last point is of high importance - the elbows are moved by actoion of the deltoids and trapezius, and not by strongly flexing the arm. Doing so will affect the barbell path away from the vertical, and so the arms are simply allowed to bend.
During this movement the torso is also inclined slightly backwards but not with the intent of pulling the barbell upwards or backwards. The movement should be carried out so as to help move the torso away from the barbell to move under. This is again reactionary - any elbow tug where the biceps are remaining relaxed will allow the barbell to continue its path upwards and lean the torso backwards. The body should be moving downwards at this point and the continuing movement of the barbell and positioning of the elbows pulls the torso back to vertical as the body descends, once the elbows have reached their highest point paralell to the ground. The continuing action of the elbows at the point will simply throw the lifter off balance, and so the body aligns towards upright as the arms forcefully extend overhead to push the body down, but not the barbell up. If this elbow movement and extension is correctly performed, the lifter should barely feel the weight of the barbell.

During this time the knees also flex to allow the hips to get low and forwards. This is achieved by moving into the deep squat position:
The feet flat on the floor, the legs are bent as the shins are tilted forwards. The hips at this point are slightly behind the heels. As the lifter continues this descent the knees will move outwards and much forwards past the toes as the torso moves to upright and the hips move down to rest on the backs of the heels and as close as possible to the centre of the base. This is the strongest position for receiving the barbell overhead.

While entering the bottom position, the quadriceps are used to brake the movement, whilst the arms are bringing the bar to lockout. The lockout occurs from the end of the elbow tug. As the body moves to vertical, the arms are driven up as previously mentioned, and the grip is rapidly tightened with the base of the palm driven in under the bar. This results in a slight backwards movement of the bar as the wrist is forced to flex backwards, which occurs at the highest and therefore slowest part of barbell travel. The barbell is directly over the base of support as the final arrangement of the hips occurs, with at least the upper half of the torso upright, not leaning forwards, and the lifter sitting with the hips inwards.

Then follows the recovery movement which is often the most overlooked part of proper technique. This part of the movement is made difficult as:
The centre of gravity of the system is now at its highest point.
The legs are fatigued from the lift.
The lifter must maintain balance whilst moving and securing the barbell overhead.

Therefore, the method of recovery needs to be extremely efficient and emphasis placed on balance. The barbell itself must remain directly over the centre of the base during the whole movement. In order to achieve this, the body joints must be moved to create a balanced link while creating upright force. This is achieved by beginning the movement by driving the feet through the floor and slowly moving the hips backwards to counter the forward shift of balance that the forward position of the knees creates. a the lifter approaches the middle portion of the movement, the hips are driven forward but not completely and the knees back. The final position will see the lifter with a slight lumber arch on the back with the bar directly over the centre of base.

The lifter positions their body into the correct start position. The hook grip should be employed to resist the spin of the bar.
The lifter begins the movement by driving the flat feet into the floor vigorously. The position of the back is maintained through isometric tension, the shoulders held fowards and with the arms allowed to hang relaxed.
The lifter eases the bar backwards through flexion of the wrist joint towards the shins.
Extension of the legs continues with the bar rising close the vertical past the knee joint, accelerating the motion.
The stretch reflex of the hamstrings begins to straighten the torso and pull the knees and hips down and forwards.
The hips and knees are driven vigorously back to the vertical position creating a large upward force.
The lifter slightly loosens the grip.
The force rips the feet from the floor in a peeling motion and the lifter rearranges the feet to the receiving position whilst simultaneously tugging the elbows up and pulling the body down.
The feet flat on the floor, the lifter descends rapidly into the deep squat pushing the body down by forcefully extending the arms overhead, and snapping the grip closed. At the same moment the knees are shifted out over the toes and the hips in to the heels.
The deep squat is achieved and the lifter begins to ascend either with the aid of the stretch reflex or after ensuring balance.
The lifter begins to ascend by pushing through the feet and easing the hips back, then driving upwards by bringing the knee and hip joints to the midline.

Notes

The lifter should practice holding both the start positions and unladen deep squat frequently.
It is important not to have unnecessary tension in the muscles before lifting.
During the first upward movement, the bar should not be pulled into the body, only eased backwards before the first straightening of the legs.

Training Notes

General [selected notes - J.H.]

The lifter, during training, should note the following to improve technique and performance:

Sets should be brief, i.e. sets of 3 or fewer lifts. Ideally only singles or doubles. Technically it is difficult to maintain the correct movement through high rep sets.
It is not advisable to use weights below 75%, or better 80% of maximum, as this is not helpful in strengthening correct technique. Neurologically, light weights are lifted differently not utilising all motor units, and lighter bars will travel higher, not preparing the lifter for gaining the deeper squat require for a heavier bar.
Technique should be reinforced through a high frequency of practice, maximising total volume of correctly performed lifts.

Fatigue in training can be spotted through the following means:
Loss of correct technique.
Slow speed of motion.
Failure to maintain balance.
These signs should tell the coach and lifter that further practice of the lift in that session should not be carried out.

In contrast, if the above signs are absent, but the lifter misses attempts at heavy weights, practice may still continue but adjusting the weights used based on the new daily maximum [see discussion on daily maximums and training maximums].

Snatch

Due to the more technical nature of the snatch over the clean, practice of this movement should occur first in any multi-lift training session, when the nervous system is 'freshest'.

Warm ups prior to lifting should be specific to the movements of the snatch, with emphasis placed on the specific joint movements. Hip jumps, bottom squats and bar swing downs are of particular use [see discussion of assistance exercises and drills].

This falls in line with how I have heard various good British lifters and coaches describe the lifts.

It's interesting to compare this with how the lifts are generally taught on this forum, the main difference seems to be that in the article it emphasises the hips moving towards the bar and here it is the other way around.

There's a second reason which also comes to mind which is reducing the weight arm in a lever. Bringing the hips, which act as a fulcrum, closer to the weight increases the force which can be applied to the bar without shifting balance of the system.